Fayochytriomyces, a new genus within Chytridiales.

Chytriomyces is a complex genus in Chytridiales. The morphological concept of the genus expanded as new taxa were added, and studies of zoospore ultrastructure and molecular phylogenies have revealed the genus to be polyphyletic. One problematic taxon is C. spinosus Fay, a distinctive species characterized by whorls of spines on the zoosporangium and a large accumulation of vesicle material beneath the operculum. With light-, scanning-electron and transmission-electron microscopy, we examined a culture (WJD186) isolated from a muck sample collected from a temporary forest pond. We also analyzed the D1-D2 variable domains of the nuc 28S rDNA (28S) sequences to confirm the phylogenetic placement of the species relative to the type of Chytriomyces, C. hyalinus Karling. The morphology of culture WJD186 is consistent with features Fay described for C. spinosus, and the zoospore ultrastructure is consistent with the Group I-type zoospore characters of Chytriomycetaceae (Chytridiales). In our molecular phylogeny C. spinosus does not group with the type of Chytriomyces. Consequently, we erect a new genus in Chytriomycetaceae and present the new combination Fayochytriomyces spinosus.

Pseudorhizidium is a new genus with distinct zoospore ultrastructure in the order Chytridiales.

A chytrid isolate (JEL 221) we identified as the rarely reported species, Rhizidium endosporangiatum Karling, was cultured axenically for the first time. The purposes of this study are to characterize the developmental morphology of isolate JEL 221 and to elucidate its zoospore ultrastructural features. Thallus development and morphology of isolate JEL 221 are characteristic of R. endosporangiatum as it was originally described. However, thallus morphology of R. endosporangiatum is not entirely typical of the genus Rhizidium, especially that of the type R. mycophilum. The presence of an endosporangium, a layer of material encapsulating the edges of the protoplast protruding through multiple discharge pores, makes this a distinctive species. Consistent with its published molecular-based phylogenetic placement, we found that isolate JEL 221 shared ultrastructural features with the two major zoospore types described for the Chytridiales but had distinct zoospore architecture. A new genus, Pseudorhizidium, is erected for this chytrid based on its thallus morphology, molecular phylogenetic placement and unique zoospore ultrastructure. This new genus does not fit into either of the described families (Chytridiaceae or Chytriomycetaceae) in the Chytridiales because of its unique zoospore ultrastructure, especially the two-layered nature of the electron-opaque plug in the base of the flagellum.

Rediscovery of an unusual chytridiaceous fungus new to the order Rhizophydiales.

The newest order in Chytridiomycota, Rhizophydiales, shows remarkable genetic divergence and zoospore ultrastructural diversity. From submersed mud from a marsh near an oligotrophic lake in the Patagonia region of Argentina, we isolated a previously undescribed chytrid in Rhizophydiales with unique 28S rRNA and ITS1-5.8S-ITS2 sequences and a distinctive zoospore and thallus. In a combined LSU + 5.8S phylogeny of representative taxa in the order, the nearest relative to this new species is Rhizophlyctis harderi, and their zoospores share several similar character states. A new genus is erected for this chytrid, the first to be brought into pure culture from this region.